1. Field of the Invention
The present invention relates to a multicast packet transferring apparatus used to transfer multicast packets between domains, a multicast packet transferring system made up of a plurality of the multicast packet transferring apparatuses and a computer readable storage medium used in each of the multicast packet transferring apparatus in the multicast packet transferring system.
The present application claims priority of Japanese Patent Application No. 2000-052446 filed on Feb. 28, 2000, which is hereby incorporated by reference.
2. Description of the Related Art
FIG. 8 is a block diagram showing configurations of a conventional multicast packet transferring system. As shown in FIG. 8, information provided by a rendezvous point (hereinafter referred simply to as “transmitter information”) is exchanged between different multicast routing control domains (“routing control domain” being hereinafter referred simply to as a “domain”), a domain 10 and a domain 20 controlled in accordance with a core-based multicast routing protocol (hereinafter referred to as a “multicast routing protocol”) including, for example, a PIM-SM (Protocol Independent Multicast-Sparse Mode).
Each of the domain 10 and domain 20 is provided with a multicast packet transferring apparatus (hereinafter referred simply to as a “transferring apparatus”) serving as a rendezvous point. Each of the transferring apparatuses receives the transmitter information from a transmitter and, if there are receivers within the domain 10 or domain 20 having received the transmitter information, by being joined to the transmitter, establishes a multicast path between the transferring apparatus having received the transmitter information and the transmitter, across a boundary of the two domains, domain 10 and domain 20. Moreover, the multicast packet transferring system is disclosed, for example, in “Internet Draft by IETF (Internet Engineering Task Force) (“draft-ietf-msdp-spec-00” by Dino Farinacci et al., December 1999).
However, the conventional technology has following problems:
A first problem is that a transfer of the multicast packet through the domain not supporting the multicast routing protocol is impossible. A reason is that, since the multicast routing protocol joins in a hop-by-hop manner between the receiver and the transmitter, it is necessary that all routers connected between the receiver and the transmitter are capable to process joining of the multicast routing protocol.
A second problem is that, since the multicast packet cannot be transferred between domains through a path being different from a unicast path, a multicast path between domains cannot be established explicitly. A reason is that, since the multicast path is established by the joining of the multicast routing protocol, the multicast path is always established in a direction opposite to the unicast path formed from a receiver side to a transmitter side and that a multicast router positioned nearest to a receiver having received packets whose numbers have exceeded specified level switches to a path not passing through a rendezvous point and changes the multicast path by being joined directly to the transmitter as shown in FIG. 8. Because of this, if the unicast path formed from a rendezvous point side to the transmitter side is different from that formed from the receiver side to the transmitter side, as shown in FIG. 8, a duplicated flow of data between domains may occur. Such a policy to provide the unicast path whose going path and returning path are different from each other between the domains cannot be applied.
A third problem is that a policy to transfer multicast packets between domains cannot be managed at all. A reason is that the multicast routing protocol does not provide such a policy management mechanism.